Immobilization of California sea lions using medetomidine plus ketamine with and without isoflurane and reversal with atipamezole

The use of medetomidine and ketamine, alone and in combination with isoflurane, with atipamezole reversal was evaluated for immobilizing 51 California sea lions (Zalophus californianus) for a variety of medical procedures at a rehabilitation center in northern California (USA) between May 1997 and August 1998. Animals were given 140 microg/kg medetomidine with 2.5 mg/kg ketamine intramuscularly. Mean (+/-SD) time to maximal effect was 8+/-5 min. At the end of the procedure, animals were given 200 microg/kg atipamezole intramuscularly. Immobilization and recovery times were, respectively, 25+/-12 and 9+/-7 min for 35 animals maintained with medetomidine and ketamine alone and 58+/-30 and 9+/-9 min for 16 animals intubated and maintained with isoflurane. No mortalities occurred as a result of the immobilizations. Disadvantages of the medetomidine and ketamine combination included a moderate variation in time to maximal effect and plane of sedation, a large injection volume and high cost. However, this combination offers safe and reversible immobilization that can be easily administered by the intramuscular route and that produces a plane of anesthesia that is sufficient to carry out most routine diagnostic procedures.     

Field immobilization and euthanasia of American opossum

Seventeen recently trapped opossum, Didelphis virginiana, (median weight 2.45 kg; range = 1.6-5.0 kg; quartiles = 1.8-3.3 kg) were immobilized with either telazol (15 or 30 mg/kg) or a mixture of medetomidine (100 micrograms/kg), butorphanol (0.2 mg/kg), and ketamine HCl (10 mg/kg) based on estimated weights. Anesthetized animals were subjected to cardiac puncture for blood withdrawal and toe pinch. Euthanasia was accomplished by intracardiac administration of 1 ml of concentrated pentobarbital sodium/phenytoin solution. Weights were underestimated for 14 of 17 animals, but were within 0.5 kg of the actual weight. Both drug combinations provided rapid and calm immobilization. Median time to recumbency for the medetomidine-butorphanol-ketamine group (n = 5) was 6 min (range = 4-10 min; quartiles = 6 and 8 min). The median time to recumbency was not statistically different for the low (n = 6) and high dose (n = 6) telazol groups, 3 and 3.5 min respectively (quartiles 3; 3.5 and 4; 5.5 min). The stronger heart beat with telazol immobilization facilitated cardiac puncture. All five animals administered the medetomidine-butorphanol-ketamine mixture and three of six animals given the low telazol dose reacted to cardiac puncture. Only one of six animals given the estimated 30 mg/kg dose of telazol reacted slightly to cardiac puncture. We conclude that 30 mg/kg telazol provides sufficient immobilization and analgesia to allow accurate cardiac puncture of the opossum if the procedure is performed within 5 to 10 min of recumbency. Intracardiac administration of concentrated pentobarbital sodium/phenytoin solution followed by bilateral thoracotomy provides appropriate euthanasia suitable for field situations.     

Immobilization of Chacoan peccaries (Catagonus wagneri) using medetomidine, Telazol, and ketamine

A combination of medetomidine, Telazol, and ketamine hydrochloride was used to immobilize captive Chacoan peccaries (Catagonus wagneri) for translocation within Paraguay during August-October 2002. Animals were darted in enclosed areas of varying size. The average dose used was 32.5+/-7.2 microg/kg of medetomidine, 0.63+/-0.2 mg/kg of Telazol, and 3.9+/-0.65 mg/kg of ketamine. First effects were noted at 4.3+/-2.1 min, and ability to handle the animals was achieved by 12.6+/-3.7 min. Heart and respiratory rates declined and oxygen saturation increased during anesthesia. Muscle relaxation was good. Atipamezole was used to antagonize the medetomidine, although recoveries were still slow. This drug combination provided adequate immobilization of Chacoan peccaries; however, this protocol would not be considered to be reversible, and confinement during recovery is recommended.     

Comparison of intravenous medetomidine and medetomidine/ketamine for immobilization of free-ranging variable flying foxes (Pteropus hypomelanus)

Medetomidine (0.03 mg/kg) and medetomidine/ketamine (0.05/5.0 and 0.025/2.5 mg/kg), administered by intravenous injection, were evaluated for short-term immobilization of wild-caught variable flying foxes (Pteropus hypomelanus). Medetomidine alone produced incomplete chemical restraint and a stressful, prolonged induction. Both ketamine/medetomidine doses produced a smooth induction and complete immobilization. The combined medetomidine/ketamine dose of 0.025/2.5 mg/kg produced a rapid induction (232±224 sec) with minimal struggling and vocalization, a complete and effective immobilization period, and tended to lead to a faster and better quality recovery than medetomidine alone or a higher dose of medetomidine and ketamine (0.05/5.0 mg/kg), thus reducing holding time and permitting an earlier release of the bat back into the wild.     

Short duration anaesthesia with medetomidine and ketamine in cynomolgus monkeys

Cynomolgus monkeys were anaesthetized with either intramuscular ketamine (10 mg/kg or intramuscular ketamine 2 mg/kg and medetomidine 50 microg/kg. Various physiological measurements were made once the animals were safe to handle and again 10 min later. Cardiovascular and respiratory function were well maintained with both regimens but the heart rate was lower and arterial-alveolar carbon dioxide gradient was higher in the animals that received medetomidine. In those animals that received medetomidine, atipamezole was given to reverse the medetomidine but there was no difference in recovery times between the two regimens. Anaesthesia was not entirely reliable with medetomidine/ketamine and we recommend caution when using this mixture.     

Optimal medetomidine dose when combined with ketamine and tiletamine-zolazepam to immobilize white-tailed deer

Chemical immobilization is often needed for safe and effective capture and handling of wildlife. We evaluated medetomidine (125, 150, 175, or 200 μg/kg; for synergistic effects and relaxation) mixed with ketamine (1.5 mg/kg; for relatively shorter recovery) and tiletamine-zolazepam (1.0 mg/kg; for rapid induction) in 22 female white-tailed deer (Odocoileus virginianus) at the University of Georgia Whitehall Deer Research Facility in Athens, Georgia, USA, on 14-15 and 21 May 2009. Deer were weighed before treatment, hand-injected intramuscularly (IM) while restrained in a squeeze chute, and released into a pen for monitoring. We measured rectal temperature, respiration rate, heart rate, hemoglobin saturation (using pulse oximetry), and arterial blood gases at 0, 10, and 20 min postimmobilization. We found no differences in induction time with different doses of medetomidine. Deer became laterally recumbent for all treatments combined at a median of 4.2 (2.6-21.3) min and were approachable by a median of 4.8 (3.5-21.8) min. Twelve of the 22 deer had rectal temperatures >40 C at time 0 and were treated with a cold-water enema. Hemoglobin saturation, estimated using pulse oximetry, was 79.5, 82.0, and 82.3% at times 0, 10, and 20, respectively. We injected atipamezole (0.35 mg/kg, IM) for reversal. Recovery occurred sooner and was more consistent for 125 and 150 μg/kg medetomidine whereby deer stood with minimal sedation to moderate ataxia within 60-90 min after atipamezole administration. We recommend using 150 μg of medetomidine with ketamine (1.5 mg/kg) and tiletamine-zolazepam (1.0 mg/kg) to provide effective and safe chemical immobilization of white-tailed deer.     

Reversible immobilization of eurasian otters with a combination of ketamine and medetomidine

The efficacy and safety of the combination of medetomidine and ketamine was examined in order to establish an adequate chemical immobilization protocol in the Eurasian otter (Lutra lutra) for use during translocation projects in Spain. Thirty-eight Eurasian otters ranging in body mass from 3 to 8.7 kg (mean 5.3 kg) were successfully anesthetized on 82 occasions. The dosage of ketamine was 5.1+/-0.8 (3.4-6.6) mg/kg (mean +/- SD; range) combined with medetomidine at a dosage of 51+/-8 Rg/kg (34-66 microg/kg). In most cases anaesthetic effect occurred within 3 min and the mean induction time was 5.5+/-3.2 min. The mean pulse rate was 95 beats/min. The mean respiratory rate was 32 respirations/min while the relative oxyhemoglobin saturation was 93%. According to these results, this anesthetic protocol is considered safe and can be recommended in wild caught Eurasian otters for immobilization during translocation projects. It is safe, rapid and can be reversed when needed with atipamezole. However caution is required as heart depression resulting in bradychardia may occur.     

Effective immobilizing doses of medetomidine-ketamine in free-ranging, wild Norwegian reindeer (Rangifer tarandus tarandus)

Combinations of medetomidine and ketamine were evaluated in free-ranging, wild Norwegian reindeer (Rangifer tarandus tarandus) as part of a reintroduction program in southwestern Norway in November 1995 and November 1996. The drugs were administered by dart from a helicopter. The mean (SD) effective immobilizing doses for 29 adults (8 males, 21 females) were 0.21 (0.04) mg medetomidine/kg and 1.0 (0.2) mg ketamine/ kg based on estimated body mass. There was no significant difference in mean induction times between males and females. However, animals with optimal hits (shoulder or thigh muscles; n=16) had a significantly shorter (P<0.05) mean induction time than did animals with suboptimal hits (abdomen or flank; n=13), 5.6 (2.2) min and 11.1 (4.7) min, respectively. Inductions were calm, and immobilized animals were maintained in sternal recumbency. Clinical side effects included hypoxemia and hyperthermia in most animals. For reversal, all animals received 5 mg atipamezole per mg medetomidine, half intravenously and half intramuscularly, and the mean (SD) time to standing was 3.7 (3.6) min.     

Experience with a naphthylmedetomidine – ketamine – hyaluronidase combination in inducing immobilization in anthropoid apes

Background The aim of the study was to compare the effect of naphthylmedetomidine to medetomidine on the behavior of orangutans and chimpanzees. Methods The immobilization was performed as part of a medical examination in five chimpanzees and three orangutans. Following pre‐medication with midazolam (0.70–1.20 mg/kg p.o.), naphthylmedetomidine (50–70 μg/kg), or medetomidine (20–30 μg/kg) was given with ketamine (3 mg/kg) and hyaluronidase (150 M.U.) into musculus deltoideus. Results We observed the distinct anti‐aggressive effect of naphthylmedetomidine. The immobilization with naphthylmedetomidine was shallower and the influence on cardiac frequency less substantial compared to medetomidine. The overall sedative effect of naphthylmedetomidine lasted for less time, and its effect was incompletely antagonized with atipamezole in comparison to medetomidine. Conclusions Naphthylmedetomidine could replace medetomidine for inducing immobilization and sedation. A combination of naphthylmedetomidine–ketamine is suitable for relocating animals to other cages or for painless medical examinations.     

Field immobilization of Molina's hog-nosed skunk (Conepatus chinga) using ketamine and xylazine

We injected 27 adult Molina's hog-nosed skunks (Conepatus chinga) intramuscularly by hand with ketamine hydrochloride (KH) and xylazine hydrochloride (XH) in the Pampas grassland of Argentina. Skunks were immobilized with a mean (±SD) dosage of 24.9±6.5 mg/kg KH and 1.9±0.6 mg/kg XH. The mean effective dosages of KH (27.6 mg/kg) and XH (1.7 mg/kg) were higher and lower, respectively, than those reported in skunks previously. Mean induction and recovery time were 5.3±1.9 min and 47.7±18.5 min, respectively. Hypothermia was the only problem detected in field immobilization and occurred in winter but did not appear to be associated with to drug doses. We conclude that KH/XH is a safe immobilizing drug combination for Molina's hog-nosed skunk.     

Use of medetomidine-ketamine and atipamezole for reversible immobilization of free-ranging hog deer (Axis porcinus) captured in drive nets

A combination of 0.05 mg/kg medetomidine and 1.5 mg/kg ketamine was used to immobilize nine adult free-ranging hog deer (Axis porcinus) captured in drive nets in the Royal Bardia National Park, Nepal, 22-23 February 2000. The drugs were administered intramuscularly from separate syringes and the mean time (+/-SD) to complete immobilization was 4.6+/-1.0 min. Muscle relaxation was good and no major clinical side effects were seen. Mean values for physiologic parameters, recorded at 10-12 and 18-20 min after drug administration, were 40.6+/-0.5 and 41.1+/-0.6 C, 87+/-5 and 84+/-4%, 107+/-16 and 113+/-16 beats/ min, and 46+/-9 and 40+/-8 breaths/min for rectal temperature, SpO2, pulse rate, and respiratory rate, respectively. All animals received 0.25 mg/ kg atipamezole intramuscularly 20-22 min after administration of medetomidine-ketamine and the mean time to coordinated running was 4.8+/-0.8 min. All animals survived for at least 5 mo post-capture. To reduce stress and to facilitate handling, medetomidine-ketamine and atipamezole are recommended for reversible immobilization of free-ranging hog deer captured in drive nets.     

Butorphanol/xylazine/ketamine immobilization of free-ranging Baird's tapirs in Costa Rica

Cardiopulmonary effects and the utility of a butorphanol/xylazine/ketamine combination were evaluated during twenty immobilizations of sixteen Baird's tapirs (Tapirus bairdii) between March 1996 and January of 1998 in Corcovado National Park (Costa Rica). The animals were attracted to a bait site and darted from tree platforms. The tapirs were estimated to weigh between 200 to 300 kg. Actual weights of three tapirs taken at later dates fell within the estimated range. A butorphanol, 48+/-1.84 (x +/- SE) mg/animal IM, and xylazine, 101+/-2.72 mg/animal IM, combination was used to immobilize the animals. In some instances, ketamine was used either IM or IV at 187+/-40.86 mg/animal to prolong the immobilization period in addition to the butorphanol/xylazine combination. Naltrexone was used IM to reverse butorphanol at 257+/-16.19 mg/animal. Either yohimbine, 34+/-0.61 or tolazoline at 12+/-10.27 mg/animal, was used to reverse xylazine. The mean time from dart impact to first visible effect was 4.63+/-0.50 min (x +/- SE). Mean time to sternal recumbency was 12.21+/-1.08 min. Mean time the tapirs were immobilized was 45.63+/-3.6 min. Mean time to return to sternal recumbency and standing in animals that received yohimbine and naltrexone was 3.16+/-1.06 and 5.33+/-1.45 min, respectively. Mean time to return to sternal recumbency and standing in animals that received tolazoline and naltrexone was 1.57+/-0.39 and 3.14+/-0.51 min, respectively. Cardiopulmonary parameters including heart rate, respiratory rate, body temperature, electrocardiogram, percent oxygen satoration, and indirect blood pressure were recorded. Arterial blood gas analysis was performed on four animals. A mild degree of hypoxemia was evidenced by low arterial oxygen saturations. Five of 14 (36%) animals measured had oxygen saturations below 90%. Bradycardia (heart rates <45 BPM) was an expected finding in 11 (55%) immobilizations. Induction, recovery and muscle relaxation of each immobilization was graded. Premature arousal, which occurred in six (30%) animals, was the only problem associated with the immobilizations. Butorphanol/xylazine is a recommended protocol for immobilization of calm, free-ranging tapirs lasting less than 30 min. Supplemental intravenous administration of ketamine is recommended for longer procedures. Nasal insufflation of oxygen is recommended.     

Antagonism of xylazine hydrochloride-ketamine hydrochloride immobilization in guineafowl (Numida meleagris) by yohimbine hydrochloride

The mean time to arousal (MTA), the mean time to sternal recumbency (MTSR) and the mean time to walking (MTW) were measured in 10 adult guineafowl (Numida meleagris) immobilized with a combination of xylazine hydrochloride (1 mg/kg) and ketamine hydrochloride (25 mg/kg). Yohimbine hydrochloride, given intravenously (1 mg/kg) at 40 min after the injection of the xylazine-ketamine, significantly shortened the MTA, the MTSR and the MTW compared to saline controls. Increasing the dosage of yohimbine to 2.5 mg/kg did not shorten recovery when compared to the lower dosage. No adverse effects were noted at either dosage of yohimbine. Yohimbine appeared to be a safe and effective antagonist of xylazine-ketamine immobilization in guineafowl and may prove useful in other avian species to produce more rapid recovery from xylazine-ketamine immobilization, xylazine sedation or xylazine overdosage.     

Evaluation of a butorphanol, detomidine, and midazolam combination for immobilization of captive Nile lechwe antelopes (Kobus magaceros)

Field immobilization of captive antelope may be required for medical examination, blood sample collection, and animal identification. The aim of this study was to evaluate the effects of a combination of butorphanol, detomidine, and midazolam (BDM) and its partial reversibility in Nile lechwe antelope (Kobus megaceros). Nine captive lechwes, weighing 28-64 kg, were immobilized, in February 2011, with butorphanol 0.20 ± 0.05 (mean ± SD) mg/kg, detomidine 0.20 ± 0.05 mg/kg, and midazolam 0.31 ± 0.08 mg/kg administered intramuscularly (IM) with a blowpipe. Physiologic parameters and depth of anesthesia were recorded when the animals became recumbent at 19.55 ± 8.36 min after darting (T0) and after 10 (T10), 20 (T20), and 30 (T30) min. An arterial blood sample was collected at T20. At the end of the procedures, immobilization was partially reversed with atipamezole 0.25 mg/kg IM. Quality of induction, immobilization, and recovery was scored. The BDM combination induced immobilization and lateral recumbency in 13.44 ± 5.61 min. Median induction score (scored 1 [excellent] to 4 [poor]) was 1 (range 1-2). Heart rate varied 40-104 beats/min, respiratory rate 16-108 breaths/min, and rectal temperature 36.5-40.3 C. Hyperthermia was observed and rapidly treated in three animals that demonstrated insufficient immobilization after darting. Arterial blood gas analyses revealed a mean pH of 7.43 ± 0.07, partial arterial pressure of CO(2) of 44.1 ± 6.0 mmHg, partial arterial pressure of O(2) of 74.0 ± 13.5 mmHg, and an arterial O(2) saturation of 94.77 ± 3.96%. Recovery was smooth and animals were walking in 13.44 ± 7.85 min. Median recovery score (1 = excellent to 4 = poor) was 1 (range 1-2). The BDM was effective in immobilizing captive healthy lechwes with minimal cardiorespiratory changes.     

Anesthesia of wild red howler monkeys (Alouatta seniculus) with medetomidine/ketamine and reversal by atipamezole

Wild red howler monkeys (Alouatta seniculus) were translocated during the flooding of the forest at a hydroelectric dam site in French Guiana. For a variety of minor clinical procedures, 96 monkeys were anesthetized with various intramuscular injections of combinations of medetomidine and ketamine. The howler population was composed of healthy animals (42 males and 54 females) of various ages. Medetomidine (150 μg/kg) associated with ketamine (4 mg/kg) gave the best results and was used on 63 animals. The injection rapidly resulted in complete immobilization with good to excellent myorelaxation. The induction stage was quiet, with absence of both corneal and pedal withdrawal reflexes in 57 animals after 2.9 ± 1.4 min. Six animals required an additional injection. Rectal temperature and respiratory and heart rates decreased during anesthesia, whereas relative oxyhemoglobin saturation increased. One death occurred during anesthesia. One abortion and one death also occurred the day following anesthesia but were more probably a result of capture stress. Atipamezole given i.m. at a dose of five times the medetomidine dose 38.4 ± 8.0 min after the anesthetic injection led to standing recovery in 7.1 ± 4.5 min. Spontaneous recovery occurred in 17 animals before the atipamezole injection after an average of 30.6 ± 9.6 min. Total recovery time was shorter in young animals. Medetomidine/ketamine induced good myorelaxation and provided considerably shortened immobilization duration, which are two notable advantages for field studies. We recommend this association for short procedures including minor surgery in red howler monkeys. Am. J. Primatol. 45:399–410, 1998. © 1998 Wiley-Liss, Inc.     

The influence of pre-anaesthetic administration of buprenorphine on the anaesthetic effects of ketamine/medetomidine and pentobarbitone in rats and the consequences of repeated anaesthesia

Rats received pentobarbitone (60, 48 and 36 mg/kg i.p.) or ketamine/medetomidine (75/100, 60/80 and 45/60 mg/microg/kg i.p.) alone, or one hour following buprenorphine (0.5 mg/kg s.c.). Animals were anaesthetized once per week for 6 weeks with one of three anaesthetic doses according to a randomized block design. In the pentobarbitone group, animals which received buprenorphine had longer sleep times (236 +/- 22 cf. 204 +/- 21 min) and longer durations of surgical anaesthesia (83 +/- 14 cf. 27 +/- 8 min) (P<0.01), these effects being potentiated with increasing anaesthetic doses (P<0.01). A greater degree of respiratory depression was found in animals that received buprenorphine (P<0.01) although this was judged clinically acceptable in all cases. Unexpectedly high mortality and a high incidence of anaesthetic complications (nine of 16 animals) in the ketamine/medetomidine group made statistical analysis of these data impossible. We conclude that for pentobarbitone, pre-anaesthetic administration of buprenorphine reduces the dose of anaesthetic required to produce surgical anaesthesia, in addition to the presumed benefits of pre-emptive analgesia. In view of the high mortality encountered, we advise caution when considering pre-anaesthetic use of opioids in combination with ketamine/medetomidine in rats.     

Total intravenous anesthesia with midazolam, ketamine, and xylazine or detomidine following induction with tiletamine, zolazepam, and xylazine in red deer (Cervus elaphus hippelaphus) undergoing surgery

Sixteen captive female red deer were successfully anesthetized to surgically implant a telemetry system. The deer were immobilized with (mean±SD) 1.79±0.29 mg/kg xylazine and 1.79±0.29 mg/kg tiletamine/zolazepam given intramuscularly with a dart gun. Anesthesia was maintained for 69±2 min using a total intravenous protocol with a catheter placed in the jugular vein. Group X received xylazine (0.5±0.055 mg/kg/hr) and group D, detomidine (2±0.22 μg/kg/hr), both in combination with ketamine (2±0.02 mg/kg/hr) and midazolam (0.03±0.0033 mg/kg/hr), as a constant rate infusion. Anesthesia was reversed with 0.09±0.01 mg/kg atipamezole and 8.7±1.21 μg/kg sarmazenil given intravenously in both groups. These drug combinations provided smooth induction, stable anesthesia for surgery, and rapid recovery. Respiratory depression and mild hypoxemia were seen, and we, therefore, recommend using supplemental intranasal oxygen.     

Transplacental transfer of medetomidine and ketamine in pregnant ewes

The extent of placental transfer of medetomidine and ketamine is unknown in pregnant ewes. Date-mated singleton (n = 8) and twin (n = 8) pregnant merino cross ewes were anaesthetized for Caesarean delivery of preterm lamb fetuses. A combination of medetomidine (20 μg/kg) and ketamine (10 mg/kg) was administered by intravenous injection and surgery performed immediately thereafter. Blood samples were collected from the ewe at one, five and 10 min after intravenous injection and from the umbilical vein of the fetus at delivery. Non-pregnant ewes were also anaesthetized (n = 8). There was no difference in the plasma concentration of medetomidine or ketamine when comparing singleton and twin ewes or pregnant and non-pregnant ewes for the short duration of the study. Fetal plasma concentrations of each drug were comparable to the maternal concentrations at the same time. We conclude that both drugs cross the placenta readily and provide anaesthesia and analgesia for the fetus when it is delivered.     

Anesthesia of boma-captured Lichtenstein's hartebeest (Sigmoceros lichtensteinii) with a combination of thiafentanil,medetomidine, and ketamine

A dose range was determined for anesthesia of recently boma-captured Lichtenstein's hartebeest (Sigmoceros lichtensteinii) (n = 13) with the synthetic opiate thiafentanil (THIA) (formerly called A3080) combined with medetomidine (MED) and ketamine (KET) in the Kasungu National Park, Malawi on 4 to 5 September 1999. The dose range of 11-29 micrograms/kg THIA (mean +/- SD = 21 +/- 4 micrograms/kg) combined with 5-10 mg/kg MED (8 +/- 1 micrograms/kg) plus 0.7-1.4 mg/kg KET (1.1 +/- 0.2 mg/kg) was found to be safe and effective for the field conditions associated with this study. The anesthesia produced by this drug combination was very predictable and characterized by a short induction time (3:34 +/- 1:20 min:sec), good muscle relaxation, and acceptable physiologic parameters for anesthesia periods ranging from 22:30-35:00 min:sec (31:14 +/- 2:50). Within the range of doses used in this study, times to onset of initial effects and recumbency were not dependent on THAI, MED, or KET doses. Anesthesia was rapidly and completely reversed by intravenous injections of naltrexone at 30 times the THAI dosage (0.69 +/- 0.19 mg/kg) and atipamezole at about four times the MED dosage (38 +/- 14 micrograms/kg). There was no residual effect from ketamine noted following reversal of THIA and MED and no mortality or morbidity was associated with this anesthetic regimen.     

Relative efficiency of succinylcholine, xylazine, and carfentanil/xylazine mixtures to immobilize free-ranging moose

We compared the efficiency of succinylcholine chloride, xylazine hydrochloride and carfentanil/xylazine mixtures in immobilizing 364 free-ranging moose (Alces alces) between 1987 and 1997 in Québec (Canada). With succinylcholine chloride (0.070, 0.062, 0.051 mg/kg of estimated body weight for calves, juveniles and adults), 63% of the 252 immobilization attempts led to complete immobilization and marking, whereas 7% of the darted animals died of respiratory paralysis during handling. The moose took an average of 13 min to lay down after darting (down time). Injection of xylazine (3.67-4.22 mg/kg) permitted sedation (the animal laid down but got up again when approached) or complete immobilization in 78% of the 40 darted adult moose, the mean down time being 8.7 min. No mortality was noted with this drug but 58% of the marked animals were only sedated. The use of RX821002A (0.058 mg/kg) as an antagonist, permitted a mean recovery time of 2.8 min after intravenous injection. With the carfentanil/xylazine mixtures (0.0071 and 0.181 mg/kg), 96% of the immobilization trials (n = 72) led to complete (88%) or partial (8%) immobilization, but 6% of the moose died several days after capture. The mean down time was 6.6 min, and injection of naltrexone (0.709 mg/kg) antagonized the effect of the immobilizing agent within 3.7 min. The respiratory rate was higher (P < 0.05) among moose immobilized with xylazine (35/min) than among those immobilized with carfentanil/xylazine mixtures (19/min) but this variation could be related to a longer pursuit time (z = 3.60; P < 0.01) and higher stress levels during handling. Rectal temperature also was higher with xylazine but the difference was small (39.7 vs. 39.3, P = 0.03) and did not differ significantly between the sexes (P > 0.05). Considering loss of materials and helicopter flight time due to non-successful marking trials, carfentanil/xylazine mixtures were the least expensive ($333 Cdn/animal).